Ethernet standards are widely used in computer networks to communicate information between computers and other electronic devices. A common family of Ethernet standards are the standards for use over twisted-pair cables, including 10BASE-T (10 Mbit/sec), 100BASE-TX (100 Mbit/sec), 1000BASE-T (1000 Mbit/sec), and 10GBASE-T (10 Gbit/sec). In general, it is desired for the higher-speed standards to support the lower-speed standards, allowing older equipment to be used if necessary, and also allowing lower-speed network management standards to be used with higher-speed standards, such as “Wake on LAN” that allows a computer to be turned on or woken up remotely by a network message.
One problem with the more recent 10GBASE-T standard is that the magnetics of the transformers used in transmitters of this standard are not fully compatible with the magnetics of transformers used by earlier, lower-speed standards. For example, legacy 100BASE-TX ports are based on transformers having an inductance of 350 uH, but 10GBASE-T performance appears to demand an inductance in the 150 uH-200 uH range for improved high frequency return loss. This is a fundamental design issue, because lowering the inductance of the transformers tends to increase the baseline wander. Baseline wander is a gradual drifting of voltage in the average receive signal caused by unbalanced data sequences sent through transformers. The 100BASE-TX standard in particular creates baseline wander due to the particular encoding used (4B5B encoding), which is unbalanced. Thus, reducing the inductance from the earlier 350 uH for systems performing under the higher-speed 10GBASE-T standard will increase baseline wander when using the 100BASE-TX standard, possibly taking the network out of compatibility with the 100BASE-TX standard. This is an issue if both 10BASE-TX and 10GBASE-T standards are used in the same network system, e.g., if multi-rate 100/1G/10GBASE-T enabled physical layer interface integrated circuits (PHYs) at the transmission end need to inter-operate with legacy 100BASE-TX ports.
Some baseline wander compensation techniques have been used in prior systems. However, such techniques are not intended for use with the magnetics needed for higher speed standards such as 10GBASE-T. In addition, the additional dynamic range available to the digital-to-analog converter (DAC) and output driver in a 10GBASE-T transmitter can be severely limited due to constraints of silicon size and power consumption, which limits any baseline wander compensation technique.
Accordingly, what is needed is a system and method that addresses baseline wander when using higher-speed Ethernet magnetics with legacy Ethernet standards, and allows for a reduction in required dynamic range needed in the transmitter for a given level of compensation.